Nowadays, liquid crystal display (LCD) is one kind of flat panel display widely used. According to a driving manner, LCD may be roughly classified as three types including a Twisted Nematic (TN) mode LCD, a Vertical Alignment (VA) mode LCD and an In Plane Switching (IPS) mode LCD.
TN mode LCD is the earliest developed LCD and its advantage is to have low cost and quick response. TN mode LCD, however, has a narrow viewing angle. On the contrary, VA mode LCD and IPS mode LCD provide a wider viewing angle so that they are better driving manner for large display devices.
Although VA mode LCD has a wider viewing angle, there exists the color washout problem. For solving this problem, a pixel circuit is divided into two sub-pixels, and pixel voltages of the two sub-pixels are different such that different brightness is generated. However, the brightness can only be restrained near gamma 2.2 curve in a certain range of gray level as shown in FIG. 1. It is not good enough, so that study for solving color washout phenomenon keeps going.